This article deals with the design and installation specifications of aFixed CO2 extinguishing system on ship. It also lists the regulations thata CO2 system on a ship has to abide by.Introduction

In the previous article we learned about the various features of carbon dioxide gasand the advantages and disadvantages attached to it. We also studied what is afixed CO2 fire extinguishing system and why it is so widely used.In this article we would go a bit more deep into the constructional and safetyspecifications related to the installation and design of the fixed CO2 system. A CO2system though efficient is extremely dangerous to the people working on the ship.Safety Of Life At Sea (SOLAS), has made special regulations regarding the usage of CO2.Probability of accidents caused due to fire is very high on ships, mainly because of high quantity of fuel oils and inflammable cargo that they carry. In case of a smallintensity fire on ship, portable fire extinguishers or other handy means of extinguishing fire can be used. But in case, the intensity of fire is high or it is humanlyimpossible to control the fire, Co2 fire extinguishing system is used.

SOLAS Regulations

CO2 usage on ships has to abide by few safety regulations, as on ship there arelives at stake and measure to fight accidents are few .The main regulations are:

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If the CO2 system is installed in the cargo spaces, the quantity of CO2 availableshould be sufficient enough to give at least a minimum of 30% of the total volume of the largest space that is protected by the CO2 system.

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If the CO2 system is installed in machinery spaces, the quantity of CO2 availableshould be sufficient to give at least a volume equal to either of the following :

a)40% of the total volume of the largest machinery spaces that is protected by theCO2 system. (The volume should exclude that part of the casing where thehorizontal area of the casing is 40% or less then the horizontal area of the spacetaken into consideration and measured midway, between tank top and lowest part of casing)b)35% of the total volume of the largest machinery spaces that are protected by theCO2 system including the area covered by the casing.

It is also a requirement that 85% of the required quantity of gas should be releasedinto the spaces within two minutes of evacuating the fire affected space.

Construction of CO2 bottles for fixed fire fighting system.

It is imperative that the CO2 bottles are strong and sturdy due to the high internalpressure they are going to withstand. For this reason, the bottles are made fromsolid drawn steel and are also hydraulically tested upto 228 bars prior to installation.CO2 is retained inside the cylinder in the liquid form under pressure.A siphon tube isprovided inside the bottle to ensure that the liquid CO2 is discharged from the bottleor else it would evaporate from the surface, giving a very slow discharge rate andtaking away the latent heat would probably cause the remaining CO2 in the bottle tofreeze.

Safety Features

Some special features are provided to the system in order to increase the safetylevel and also to make operation smooth.The control cabinet doors are installed with a special signaling system. Whenever aperson opens the door of the control cabinet in order to operate the CO2 system, analarm is sounded automatically. This is done to signal crew members of CO2flooding on ship. This is also an indication to leave the fire affected place andassemble at the muster station. A master valveis also provided on the main pipe going to the machinery or cargospaces, in order to stop the CO2 supply in case of accidental release.CO2 fire extinguishing system is installed in both cargo and machinery spaces of aship, for the chances of accidents due to fire are more. This article deals with thedesign and working of CO2 system in cargo an machinery spaces.

CO2 System In Machinery Spaces

A Co2 system of machinery spaces consists of a bank of Co2 bottles that can beoperated from a remote place located away from the machinery spaces. The systemalso consists of pilot Co2 cylinders which control the activation of the bank of Co2bottles. The Pilot cylinders are contained in a control box and are normally keptdisconnected. The system is connected to the pilot cylinders and the control box withthe help of steel wires or flexible pipes. All these pipes are fitted with a quick actioncoupling. When the system is to be activated, the coupling in plugged into thecorresponding socket. The valves of the pilot cylinders will be opened with the helpof the levers in the main CO2 control system.The Co2 from the pilot cylinders will open the system's main stop valve. The mainstopvalvehas a piston which gets depressed due to the Co2 gas pressure andallows the pilot gas to flow to the bank of CO2 cylinders. This pilot gas operates the

cylinders' valves. These valves are known as Klem valves. All these valves have anactuator which gets operated by the pilot pressure.The detection of fire is done by various sensors installed in the machineryspaces.Though the opening of control box operates an alarm, the main decision for Co2 flooding is taken by the Chief engineer, after due consultation with the master of the ship. Before releasing Co2 into the fire affected space, it should be made surethat everybody is out of the place and the place is fully enclosed i.e all skylights andventilators are closed air-tight. Pumps supplying fuel oil should also be stopped inorder to prevent re-ignition.Separate levers for each and every space are present inside the main controllingcabinet. The operating of a particular lever activates the pilot bottles, which helps inreleasing the complete bank of bottles designated for that place. With the opening of the master valve, Co2 is flooded inside the fire affected space, which then smothersthe fire with the help of blanket effect.

Co2 System for Cargo Space

The release mechanism of CO2 system in cargo spaces is same as that of themachinery spaces. The only difference is that the cargo spaces have a different typeof fire detection system.For detection of fire in cargo hold, a sample of air is drawn from all the cargo holdsby an extractor fan.This sample of air is passed through a cabinet wherein a set of smoke sensitive sensors analyze the sample. The sensors will detect any presenceof smoke in the sample. As soon as the sensor detects smoke in the sample, itactivates the CO2 alarm system of the ship. A part of the sample is also dischargedto the wheelhouse in order to cross-check the presence of smoke in the sample. Thiscan be done by smelling the smoke. The sample is later vented to the air.In order to check whether the extractor is extracting samples from the holds, a smallindicator propeller is fitted, which ensures that the samples are taken.

Precaution to be taken after the fire is extinguished.

After the fire is extinguished by the flooding system, all the doors,hatches,vents andother openings should be opened in order to ventilate the space properly, before anyentry is made into the space.The space should not be approached with any type of open flames as it mightcontain flammable vapours, which can lead to fire or explosion.

Checks on the system

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Pipes leading to the spaces should regularly be blown with air to ensure that they arenot blocked.

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The level in the Co2 bottles should be checked on regular basis. If in a particular check, the difference is 10% of the total volume, the bottle should be replaced assoon as possible.